MarkCO,

I see you offer a 18" rifle length gas barrel, have you messed with a 18" intermediate?

SA Friday, there's a handful of offerings in 16/18 barrels with intermediate gas systems. Ranier offers a few barrels as well as intermediate gas tubes.

MarkCO might know better the me, KAC might have been the 1st ones to come out with the intermediate length? Found these drawings of the KAC version, supposedly .4 shorter then the Vltor/Noveske.

http://riflebarrels.com/intermediate-gas-length-223s/